Thin film magnetoresistive (MR) read and inductive write transducers are widely used for magnetic heads in data storage devices, such as disk drives and linear tape drives. Various types of MR read heads are known in the art, including anisotropic magnetoresistive (AMR) read heads, giant magnetoresistive (GMR) read heads, and spin valve read heads. In typical magnetic tape read/write heads, multiple merged MR read/inductive write transducers are grouped into a single structure called a magnetic head cluster. Each of the transducers is typically aligned in the cluster along one edge, known as an air bearing surface (ABS) in disk drive technology and known as a tape bearing surface (TBS) for tape drives (for simplicity this surface will be referred to herein as a tape bearing surface), which faces a recording medium during normal read/write operation. In general, each transducer of a cluster provides an unique read/write channel.
The demand for data storage has been increasing in recent years and this demand has put pressure on fabrication processes for more efficient and cost effective methods and devices. In order to keep up with this demand, attempts to improve various aspects of magnetic head technology include increasing the sensitivity of the magnetic heads, reducing manufacturing costs, and simplifying manufacturing processes.
A conventional manufacturing process for fabricating a magnetic head cluster will be described next with reference to FIGS. 1 and 2. As shown in FIGS. 1 and 2, a magnetic head cluster 115 is made by forming a plurality of inner merged MR read/inductive write transducers 100 and outermost merged MR read/inductive write transducers 105, a plurality of electrical lapping guides 175, and a plurality of terminals 107 on a single wafer 110. The wafer 110 can be formed from any material which has high wear resistance, strength, fracture toughness, and good electrical conductivity, such as an alumina titanium-carbide (Al2O3/TiC) ceramic wafer. The processes used to form the transducers 100 and 105 on the wafer 110 typically include a combination of lithography, deposition (vacuum or plating), and etching steps, all of which are known in the art. The transducers 100 and 105 are grouped into the clusters 115, which are separated from one another by separation kerfs 120. As shown in FIG. 1, the clusters 115 are aligned in rows and columns defined by the separation kerfs 120. Once the process of forming the clusters 115 is complete, the wafer 110 is cut along the separation kerfs 120, dividing the wafer 110 into a plurality of clusters. This well-known process of cutting the wafer along the kerfs is commonly referred to as “dicing.”
As mentioned above, the transducers 100 and 105 included in each cluster 115 are typically merged MR read/inductive write transducers. As shown in FIG. 3, a conventional MR read transducer 125 typically includes an MR stripe 130, which exhibits variations in resistance when exposed to a magnetic field. The stripe height SH of the MR stripe 130 must be controlled within a tight tolerance, such as within a few micro-inches, so that a sensed magnetic signal can generate an optimum change in a resistance of the MR stripe 130. The inductive write transducer 135 typically comprises various layers of poles 140 and insulating material 145, and also includes an electrical coil 150. The region of the inductive write transducer 135 closest to an upper edge 155 (shown on FIG. 2) of the cluster 115, where the two poles are separated only by a thin insulating layer, is typically called a throat 160. As will be explained later, the region closest to the upper edge 155 will eventually be lapped to form a tape bearing surface. As is known in the art, the throat height TH must also be controlled within a tight tolerance for the transducer to generate an optimum magnetic signal.
When the separation kerfs 120 are formed on the wafer 110, a slight amount of excess substrate is provided along the upper edge 155 of each cluster. The reason for providing this slight amount of excess substrate is that the dicing process is not precise enough to achieve the optimum stripe height SH and throat height TH for each transducer 100 and 105. So, rather than inadvertently cutting the stripe 130 or throat 160 too short while dicing the wafer 110, the stripe 130 and throat 160 are intentionally left too long and later are carefully shortened by a process known as lapping.
FIG. 4 shows an exaggerated view of the conventional lapping process in order to provide a clear illustration. The broken line in FIG. 4 represents a portion of the cluster 115 which has already been removed by the lapping process. In FIG. 4, a controller 185 operates to activate and halt a lapping plate rotator 190. The lapping plate rotator 190, when activated, causes a lapping plate 165 to rotate relative to the cluster 115, thereby grinding the upper edge 155. Eventually, a sufficient amount of upper edge 155 is ground away to form a tape bearing surface 170. The tape bearing surface 170 is a surface of the magnetic head cluster 115 which will face a recording medium (not shown) when the magnetic head cluster 115 is used for read/write operations. A lapping plate pressure applicator 195 also receives signals from the controller 185 for continuously adjusting the amount of pressure being applied to the cluster 115 during the lapping process. The lapping plate pressure applicator 195 may include, for example, one or more dual action air cylinders (not shown) for applying varying amounts of pressure to different points on the cluster 115 in order to provide for skew control. The controller 185 senses an electrical resistance of the electrical lapping guides 175, which changes as portions of the electrical lapping guides 175 adjoining the upper edge 155 are ground away. The lapping process is complete once the portions of the cluster 115 are removed up to line A, which indicates the desired position of the tape bearing surface 170 of the cluster 115.
During the lapping process, the excess portion of the substrate 210 is carefully ground away by introducing an abrasive material, such as a diamond slurry (not shown), between the rotating lapping plate 165 and the upper edge 155 of the fixed cluster 115. In order to provide for precise control during the lapping process, the electrical lapping guides 175 are typically provided between each outermost transducer 105 and a respective outer edge 180 of each cluster 115. Once the electrical lapping guides 175 reach a predetermined resistance, the controller 185 halts the motion of the lapping plate 165. Ideally, the predetermined resistance is selected so that the target stripe height SH and throat height TH are achieved.
In general, lapping guides and separation kerfs, which are useful during the manufacturing of magnetic head clusters, have no functional purpose during normal operation of a magnetic head cluster. As mentioned above, electrical lapping guides are typically provided between an outermost transducer and an outer edge of each cluster. Thus, the size of each cluster is larger than its functional size, which need only include transducers. Therefore, from a functional standpoint, the wafer space occupied by lapping guides and separation kerfs is wasted. Moreover, in order to minimize the unit cost per cluster, efficient use of wafer space is important. For this reason, recent efforts have been made to increase the efficiency with which wafer space is utilized by reducing the amount of wafer space used for lapping guides and separation kerfs. Accordingly, separation kerfs have been reduced to a very small size so that more clusters can be put onto the same wafer.
U.S. Pat. No. 6,027,397 discloses further efforts to efficiently utilize wafer space, wherein the cluster size is reduced by putting the lapping guides onto the separation kerfs. U.S. Pat. No. 5,588,199 discloses another attempt to efficiently utilize wafer space, wherein the number of transducers per wafer is increased by adding a resistor network, which is used as a lapping guide, inside the transducers. Therefore, there is no need for a separate electrical lapping guide. A similar approach can be found in U.S. Pat. No. 5,772,493 by using an external magnetic excitation field to the transducer and measuring the resistance of the MR element in response to variations in the applied magnetic excitation field.
Despite these past attempts to increase the efficiency with which wafer space is utilized, there continues to be a need to improve wafer utilization and simplify manufacturing processes.